The context of the present invention is the family of wireless local area networks or WLANs based upon the IEEE 802.11 standards, which define intermediate devices (IDs) such as access points (APs), bridges, routers and brouters that provide access for mobile devices and to other networks, such as hard-wired local area and global networks, such as the Internet. Wireless receiving points utilized in access broadcast video streaming may include a set top box in a simple system, whereas in commercial rebroadcast system a transcoder /multiplexer/demultiplexer or TMD may operate in conjunction with a local video server. In receiving Internet data, a common gateway operating in a conventional Internet Protocol/Transmission Control ProtocolfUser Datagram Protocol (IP/TCP/UDP) protocol may be utilized.
Conventionally, the IEEE 802.11 based architecture is comprised of several components and services that interact to provide station mobility transparent to the higher layers of the network stack. The IEEE 802.11 based network defines a station as the component that connects to a wireless medium and contains the functionality of the IEEE 802.11 protocols, that being MAC (Medium Access Control), PHY (Physical Layer), and a connection to the wireless media. Typically, the IEEE 802.11 protocols are implemented in the hardware and/or software of a network interface card (NIC).
The IEEE 802.11 standards also define a Basic Service Set or BSS, which is regarded as a basic building block in WLAN architecture. The BSS consists of a group of any number of ID stations that communicate with one another. In an independent BSS, the mobile stations communicate directly with each other. In an infrastructure BSS, all stations in the BSS communicate with the ID and no longer communicate directly with the independent BSS, such that all frames are relayed between stations by the ID.
A station could be a laptop PC, handheld device, or an AP. Stations may be mobile, portable, or stationary and all stations support the IEEE 802.11 station services of authentication, de-authentication, privacy, and data delivery.
If the broadcast or multicast originator is a mobile terminal, broadcast or multicast data are first transferred from the mobile terminal to the ID in a unicast transmission. In general, a broadcast transmission is a transmission from one to all; a multicast transmission is a transmission from one to many; and a unicast transmission is from one to one. Hereinafter, broadcast and multicast will be used interchangeably. According to the IEEE 802.11 specifications, the broadcast/multicast message may be distributed into the BSS by the ID. Regardless of the length of the frame, no RTS/CTS exchange can be used. In addition, no ACK is permitted to be transmitted to the ID by any of the recipients of the multicast/broadcast frame(s). There is no MAC-level recovery on broadcast or multicast frames sent from the ID.
Video transmissions—in particular real time transmissions—require broadcast/multicast transmissions over a network, e.g., over a WLAN. However, broadcast/multicast transmissions suffer from an inherent lack of an error correction mechanism. When a data packet is sent to a group of receivers (broadcast/multicast), it is extremely difficult, if not impossible for the transmitter to manage the retransmission protocol for each receiver.
Several mechanisms exist to overcome the data packet loss in a network, in particular in a WLAN, such as automatic forward error correction (FEC), multicast automatic repeat request (ARQ) etc. All of these mechanisms, however, suffer from significant added complexity and limitations in certain network products. For example, some WLAN intermediate devices like an Access Point (AP) or a bridge, where bridge and/or AP are used herein to include router and/or brouter or any device having equivalent functionality, have an inherent limit in the transmission rate for WLAN multicast data packets on the premise that multicast quality should be limited by the client, e.g., mobile terminal with the poorest reception (i.e., the client that is farthest away from the ID). Such a limitation dictates that even if a client is close to the ID there is no possibility for any QoS upgrade of the multicast quality.